1. Field of the Invention
This invention relates to a cement dispersant. More specifically, it relates to a cement dispersant to be used in mortar works and concrete works for the purpose of improving the efficiency of operations to be performed, enhancing the strength and durability of products to be obtained, repressing the tendency of products toward cracking, and improving other physical properties of products.
2. Description of the Prior Art
Preferably, lignin sulfonates salts, such as of gluconic acid and glucoheptoic acid, naphthalene sulfonic acid-formaldehyde condensation salt, and polysaccharide have been used as cement dispersants. The lignin sulfonates are obtained from the process for production of sulfite pulp. They have the disadvantage that their water-reducing effects are dispersed and their increased incorporation of air brings about adverse effects on the physical products of mortar and concrete structures to be produced. The salts of gluconic acid and glucoheptoic acid are such that when they are added in a large amount for the purpose of ensuring high flowability, they result in considerable retardation and impairment of hardening, possibly to the extent of rendering them useless. Starch hydrolyzate is a polysaccharide type cement dispersant. When this cement dispersant is used by itself, it conspicuously shows its tendency to retard the hardening. It is, therefore, used generally in combination with calcium chloride or triethanolamine. Unfortunately, calcium chloride is harmful to the prevention of reinforcing steel bars from rusting.
Cement dispersants of the naphthalene sulfonic acid-formaldehyde condensation salt type excel in the efficiency of water-reduction and allow high flowability without entailing any considerable retardation of hardening and, therefore, they have found extensive utility as a high-range water-reducing agents for the manufacture of concrete products and as a super plasticizer for ready-mixed concrete.
Cement dispersants of the naphthalene sulfonic acid-formaldehyde condensates salt type, however, suffer from the disadvantage that the water-reducing effects are observed for only a short period and the so-called slump loss is so conspicuous that the flowability (slump) of concrete notably decreases after of 20 to 30 minutes following addition of the dispersant. In a plant for the manufacture of concrete products in which a cement composition such as mortar or concrete is conveyed under the pressure by a pump, for example, when the conveyance by the pump is sometimes suspended temporarily for a lunchtime or because of a mechanical problem. Subsequently it is restarted and the pressure for the conveyance may be sharply increased possibility to the extent of clogging the pump or inducing other similar mechanical trouble. When the cement composition is placed in a mold and the subsequent forming of the cement composition e.g. by compaction, is delayed for some reason or other, incomplete filling may result.
Furthermore, where a cement dispersant is used in the ready-mixed concrete, the incorporation of the cement dispersant cannot be carried out in the manufacturing plant for the ready-mixed concrete and must therefore be made in the immediate neighborhood of the site where the concrete to be used. Unfortunately, the high-speed agitation of the added cement dispersant in the concrete within the mixer car may well result in unacceptable noise. This cement dispersion may also cause the pump being used for the purpose of conveying the concrete to suffer from mechanical trouble or may result in incomplete filling of the mold.
An object of this invention, therefore, is to provide a novel cement dispersant.
Another object of this invention is to provide a cement dispersant which allows high flowability without entailing any appreciable retardation of hardening, which permits the high flowability over a long time, which ensures stable workability, and which excels in the ability to curb the phenomenon of slump loss.
Still another object of this invention is to provide a novel cement composition.
Yet another object of this invention is to provide a novel method for dispersing the cement.